1. Field of the Invention
The present invention relates to a driving voltage control system for a plasma display panel, and more particularly to a plasma display panel driving apparatus wherein selective discharging of cells is performed in an optimum state to display an image in an optimum voltage condition.
2. Description of the Related Art
Normally, a plasma display panel of the type mentioned performs selective discharge and light emission of pixels making use of a characteristic that there is a difference between a discharge starting voltage and a discharge maintaining voltage of gas filled between two glass plates.
For example, if a certain cell is selected so as to emit light, discharging for writing is performed for the cell in advance so that charge called wall charge is stored in a wall in the inside of the cell.
On the other hand, if a cell is selected so as not to emit light, discharging for writing is not performed, and consequently, wall charge is not accumulated.
After, from among cells of all of pixels of a plasma display panel, those cells which are to emit light depending upon presence of wall charge are selected in this manner, a discharge maintaining pulse is applied at a time to all cells.
Generally, since discharge gas used for a plasma display panel has a discharge starting voltage set higher than its discharge maintaining voltage as seen in FIG. 1, to those cells which have wall charge because a discharge maintaining pulse has been applied thereto, that is, to those cells with which writing discharging has been performed in advance, a voltage corresponding to the wall charge is applied in addition to the discharge maintaining voltage. Consequently, those cells begin to discharge and emit light.
However, those cells to which no wall charge has been given cannot enter a light emitting state only with the discharge maintaining voltage.
While light emission control of a plasma display panel conventionally makes use of presence or absence of wall charge and a difference between a discharge maintaining voltage and a discharge starting voltage in this manner, it is sometimes difficult to control all cells in an optimum state against a secular change or a temperature variation.
An exemplary one of conventional driving apparatus for a plasma display panel is shown in FIG. 5. Referring to FIG. 5, the driving apparatus for a plasma display panel shown includes a scanning electrode driver 16, a write electrode driver 11 and a common electrode driver 12 for a main scanning electrode set 50, a write electrode set 51 and a common electrode set 52 of a plasma display panel PDP, respectively. The scanning electrode set 16 includes a pulse generator 13 for generating various pulse signals, a maintaining pulse generator 14 for generating a maintaining pulse signal, and a switching circuit 15 for selectively outputting one of an output pulse signal of the pulse generator 13 and the maintaining pulse signal from the maintaining pulse generator 14. The scanning electrode set 50 is driven by a maintaining voltage (Vs) power supply 2 and drives the scanning electrode set 50 in accordance with the pulse signal selected by the switching circuit 15. Meanwhile, the write electrode driver 11 is driven by a discharging voltage (Vd) power supply 5 and drives the write electrode set 51 in accordance with a normal signal (normal image signal) originated from a normal signal inputting section 6 and processed by a signal processing circuit 10.
Consequently, depending upon a cell, if such a phenomenon occurs that, although wall charge is not formed therein, the cell discharges when only the discharge maintaining voltage is applied thereto, or although the cell has wall charge and must emit light, discharge and emission of light does not occur, this cannot be observed. In this instance, it is normally the actual state of things that it is confirmed through visual observation if those cells in the screen which should emit light do not emit light or if those cells which should not emit light emit light, and the setting of the discharge maintaining voltage or the writing voltage is adjusted manually.
Therefore, where it is necessary to adjust the discharge maintaining voltage or the writing voltage in accordance with the necessity upon manufacture of the product or when the situation of a discharging phenomenon varies because of a secular change or from some other reason, the adjustment operation is cumbersome and besides requires long time.